The present invention relates to a stacked semiconductor device which comprises a plurality of stacked monocrystalline semiconductor films each of which has a plurality of semiconductor elements.
Such a stacked semiconductor device wherein the plurality of stacked monocrystalline semiconductor films of the same material between which insulating layers are sandwiched is very promising as a photo semiconductor device and as a three-dimensional integrated circuit.
FIG. 1 is a sectional view of a conventional stacked semiconductor device. Referring to FIG. 1, reference numeral 10 denotes a monocrystalline semiconductor substrate; and 11a, 11b and 11c, first, second and third monocrystalline semiconductor films. Reference numerals 12a, 12b and 12c denote insulating films respectively between the semiconductor substrate 10 and the first semiconductor film 11a, between the first and second monocrystalline semiconductor films 11a and 11b, and between the second and third monocrystalline semiconductor films 11b and 11c. Reference numerals 13a, 13b and 13c denote connecting regions respectively between the semiconductor substrate 10 and the first monocrystalline semiconductor film 11a, between the first and second monocrystalline semiconductor films 11a and 11b, between the second and third monocrystalline semiconductor films 11b and 11c. Reference numerals 14a, 14b and 14c denote first, second and third isolating layers respectively formed in the first, second and third monocrystalline semiconductor films.
FIGS. 2A to 2E are sectional views for explaining the steps of manufacturing the stacked semiconductor device shown in FIG. 1. The semiconductor elements formed in the monocrystalline semiconductor substrate and the monocrystalline semiconductor films throughout FIGS. 1 to 9F are not directly related to the present invention, so that the description and illustration thereof will be omitted for descriptive convenience.
Referring to FIG. 2A, the first insulating film 12a is deposited on the semiconductor substrate 10 except for the connecting region 13a. As shown in FIG. 2B, a polycrystalline or amorphous semiconductor film is deposited on the first insulating film 12a. Thereafter, annealing such as laser annealing is performed to grow single crystals using the connecting region 13a as a seed crystal. As a result, the first monocrystalline semiconductor film 11a is formed.
As shown in FIG. 2C, the second insulating film 12b is then deposited on the first monocrystalline semiconductor film 11a except for the connecting region 13b. As shown in FIG. 2D, a polycrystalline or amorphous semiconductor film is deposited to cover the entire surface. Thus, in the same manner as the first monocrystalline semiconductor film 11a, the second monocrystalline semiconductor film 11b is obtained. Similarly, as shown in FIG. 2E, the third insulating film 12C is deposited on the second monocrystalline semiconductor film 11b except for the third connecting region 13c. The third monocrystalline semiconductor film 11c is then formed to obtain the structure shown in FIG. 1.
In the conventional method for manufacturing the stacked semiconductor device and the thus obtained semiconductor device, the following drawbacks are presented. It is important to convert the polycrystalline or amorphous semiconductor film to a monocrystalline semiconductor film using part of the semiconductor substrate or part of the underlying monocrystalline semiconductor film as a seed crystal. However, since the polycrystalline or amorphous semiconductor film is formed on the insulating layer, the above conversion is difficult to accomplish at a location which is apart from the seed crystal. In the conventional stacked semiconductor device, the position of the seed crystal has only been selected in accordance with the element or circuit configuration. For this reason, the first, second and third connecting regions 13a, 13b and 13c which are used as the seed crystals for forming the first, second and third monocrystalline semiconductor films 11a, 11b and 11c are spaced far apart from each other. When the number of monocrystalline semiconductor films to be stacked is increased, the distance for conversion into single crystals from the semiconductor substrate is increased from what is regarded as the initial seed crystal. Therefore, conversion into single crystals can hardly be achieved. In this condition, almost impossible control conditions of annealing or the like are required for conversion into single crystals. Furthermore, even if the stacked monocrystalline semiconductor structure is obtained by the above process, the crystal quality of the upper semiconductor films is greatly degraded. For example, the carrier mobility is greatly degraded.